[R] Oddity with names

[Liaw, Andy]

You asked R to create a new data frame MyFrame[,1:3] (note: you don't need
the c()), then change the names of this data frame.  Since you didn't ask R
to store this in an object, it gets discarded.  Constructions such as 

  names(MyFrame[,1:3]) <- something

simply won't work as you expected, and even if it worked, would be much less
efficient than

  names(MyFrame)[1:3] <- something

because you are simply assigning names to some columns.  There's no need to
ask R to extract those columns out of the data frame.

Andy

> -----Original Message-----
> From: Andrew Robinson [mailto:andrewr at uidaho.edu]
> Sent: Thursday, July 18, 2002 12:07 PM
> To: ripley at stats.ox.ac.uk
> Cc: r-help at stat.math.ethz.ch; Robert Keefe
> Subject: Re: [R] Oddity with names
> 
> 
> At 08:01 AM 7/18/2002 +0100, Brian D. Ripley wrote:
> >On Wed, 17 Jul 2002, Andrew Robinson wrote:
> >
> > > Hi all,
> > >
> > > I'm using R 1.5.1 on Windows 2000.  The following snippet 
> of code doesn't
> > > seem to do anything - no error is reported, and there is 
> no name change.
> > >
> > > names(myFrame[,c(1:3)]) <- c("name1", "name2", "name3")
> > >
> > > This code however works nicely:
> > >
> > > names(myFrame)[c(1:3)] <- c("name1", "name2", "name3")
> > >
> > > Can anyone suggest why the first doesn't work?  Ought an 
> error be reported?
> >
> >It does work.  It creates a new object myFrame[,c(1:3)] and 
> changes its
> >names.  That's not what you wanted, but R is your servant 
> not your master
> >and does allow you to do such things.
> 
> I'm sorry but I'm still confused.  Do you mean that another 
> object called 
> myFrame is created, with the new names?  It doesn't appear in 
> the objects() 
> list.  The original is still there, within unchanged names.
> 
> Andrew
> 
> Andrew Robinson                  Phone: 208-885-7115
> Department of Forest Resources   Fax:   208-885-6226
> University of Idaho              E: andrewr at uidaho.edu
> Po Box 441133                    WWW: http://www.uidaho.edu/~andrewr
> Moscow, ID 83843                 and: 
http://www.biometrics.uidaho.edu/
No statement above may be construed to necessarily represent my employer.

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